Method and apparatus for information recording and reproduction of a pit-shape-forming optical recording type

ABSTRACT

A method and an apparatus for recording and reproducing information for use with an optical disk apparatus in which a pit edge recording method is used. According to the pit edge recording method, the leading edge and the trailing edge of a hole pit or a record domain generated during a recording operation are dealt with as information. During the recording, the recording pulse width and the recording power are corrected, and during the reproduction, the variation in the edge position is corrected.

CROSS-REFERENCE OF THE RELATED APPLICATION

This application relates to an application U.S. Ser. No. 878,436entitled "Method and Apparatus for Recording and ReproducingInformation" and assigned to the present assignee, based an JapanesePatent Application No. 60-144751 filed July 3, 1985.

BACKGROUND OF THE INVENTION

The present invention relates to a method of recording and reproducinginformation and an apparatus for recording and reproducing informationon and from an optical disk, and in particular, to a method of recordingand reproducing information and a apparatus for recording andreproducing information on and from an optical disk using a pit edgerecording method suitable for improving a recording density.

A method of demodulation for demodulating recording data by detecting aleading edge and a trailing edge of a change in a quantity of areflected light (i.e. a waveform of a reproduced signal) obtained froman optical disk has been adopted for a digital audio disk (DAD). Theprinciple of the data demodulation is described e.g. in "Introduction toVideo Disk and DAD" by Iwamura (Corona Publishing Co. Japan), pp.212-215. The demodulation is achieved by detecting variation points inthe waveform of the reproduction signal, namely, the leading edge andthe trailing edge thereof and producing a detection window from theleading edge and the trailing edge so as to attain reproduced data.According to the demodulation method used for the DAD, a correctdemodulation is conducted under the conditions that assuming a datainterval to be T, the detection window width is T/2 and the pulserepresenting variation points are located in a region of ±T/4.Consequently, an error occurs if a zero cross point (corresponding to avariation point) and is moved due to a noise, a waveform distortion, arotation jitter, an eccentric jitter, etc. to be beyond the detectionwindow. Although the leading edge and the trailing edge can be used asdata in an optical disk of la write-once type, since an object disk forthe recording and reproducing operations is directly irradiated withlaser light pulses to effect a thermal recording thereon in a case ofthe write-once type disk, the positions of the leading edge and thetrailing edge of a recording region (a pit or a magnetic domain) arelikely to be easily influenced by a sensitivity characteristic of arecording medium and a jitter consequently, the positions are apt to beindefinitely shifted. In the case of the DAD, since the pits aremanufactured in a photoresist forming process when the disk is produced,such a problem has not arisen.

When applying the pit edge recording system to an optical disk of thewrite-once type or an erasable type, it is essential to correct the edgeshift of the leading edge and the trailing edge in any cases during arecording operation.

SUMMARY OF THE INVENTION

According to the types of the disk above like the DAD, the informationpits are beforehand produced when the disk is manufactured, and hencethe amount of edge shift hardly causes a problem and the stabledemodulation can be achieved. However, for recording medium such as anoptical disk of the write-once type, a magneto-optical disk, an opticaldisk of phase-transition type in which a recording pit is directlyformed in a recording film of an object disk with a thermal energy of abeam spot, the pit edge recording method using the edges as data has notbeen put to practical uses. This is because the pits formed are apt tobe influenced by the sensitivity characteristic of a recording medium, alinear speed thereof, and the like. Since the pit formed by a thermalrecording operation has an expanded area due to an influence of a heatdiffusion, the positions of the edges thereof cannot be easilycontrolled.

It is therefore an object of the present invention to provide a methodand an apparatus for recording and reproducing information in which in arecording and reproduced method using as data the leading-edge and thetrailing edge of a recording pit, the variation in the recordingcharacteristic is minimized to enable highly reliable data recording andreproducing operations with a reduced edge shift and a pit edgerecording advantageous for a high-density recording can be effected witha stability also on a medium of the thermal recording type.

According to the present invention, in order to properly control theedge positions, the recording pulse width and power are continuouslyoptimized with respect to the characteristic of the recording medium andthe recording position. The medium itself is desired to have a linearcharacteristic or the like for the variation of a reproduction pulsewidth with respect to the recording pulse width. In addition, thevariation in the edge position not removable during the recordingoperation is to be eliminated during the reproduction.

In an operation to effect a correction during a recording operation, forthe object position on a disk, information beforehand generated andstored in a header thereof or information detected by use of an externalscale is used. Alternatively, both of the information items may be used.Moreover, if a type, a sensitivity characteristic, and the like arebeforehand recorded in the header section, the correction can beachieved with an improved accuracy This enables the recording pulsewidth and power to be easily and properly set. In a correction for areproducing operation, when recording user data on a disk, a duplicatedsynchronization signal is simultaneously recorded preceding the userdata. A time difference between a detection signal attained from aseries of leading edge data of the synchronization signal and adetection signal obtained from a series of trailing edge data isdetected to effect a time-axis correction on user data in the succeedingsector, which reduces influences from the edge variation and theunevenness of reflection not removable only through the correction inthe recording operation. As described above, the amount of edge movementis corrected during the recording and the quantity of variation in the.edge position is corrected during the reproduction, thereby enablingstable recording and reproduction of information.

Incidentally, in U.S. Pat. No. 4,646,103, there has been described asystem in which the pit edge recording method is applied to a recordingmedium of the thermal recording type.

According to U.S. Pat. No. 4,646,103, for a recording pulse with a longpulse width having a strong influence of the heat diffusion, in order toprevent the effect of the heat diffusion with respect to a portion of apit or a magnetic domain ranging from the leading edge to the trailingedge thereof, the recording pulse signal includes two pulses each havinga short pulse width and respectively representing the leading edge andthe trailing edge of a demodulation signal pulse.

When the interval between these two pits or magnetic domains (i.e. aspatial interval associated with the time interval between the recordingpulses) is less than an optical resolution of the light beam for thereproduction, a hollow of a reproduced waveform corresponding to theinterval between two pits or magnetic domains is at a level higher thana slice level. Namely, in this case, the two pits or magnetic domainsare reproduced as a consecutive pit or magnetic domain

When the interval between these two pits or magnetic domains is not lessthan the optical resolution of the light beam for the reproduction,between two recording pulses, there is supplied a laser output with amagnitude not giving an influence of the heat diffusion to the trailingedge of the succeeding pit thereof or there is inserted at least a pulsehaving a short pulse width. The interval of the inserted pulses are socontrolled that the interval between the pits or magnetic domains formedby these pulses is less than the optical resolution of the reproducinglight beam. This provision causes the hollow of the reproduced waveformcorresponding to the interval between the pits or the magnetic domainsto be retained at a level higher than the slice level and hence aplurality of pits or magnetic domains can be reproduced as a successivepit or a successive magnetic domain. Incidentally, during thereproduction, the signals associated with the leading edge and thetrailing edge of recording information are respectively detected in anindependent fashion so that the timing signal is independentlyreproduced respectively from each of the obtained signals and the datareproduction is effected according to the timing signals.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be apparent from the following detaileddescription taken in conjunction with the accompanying drawings inwhich:

FIG. 1 (a-f) is an explanatory diagram useful for explaining the pitedge recording method;

FIG. 2 is a schematic diagram illustrating relationships between pitsformed and the distance of beam movement;

FIG. 3 is a schematic diagram illustrating relationships between therecording power and the quantity of variation in the recording timing;

FIG. 4 is an explanatory diagram useful for explaining the influence ofthe heat diffusion;

FIG. 5 is a schematic diagram illustrating the fundamental configurationof an optical disk apparatus to which the present invention is applied;

FIG. 6 is a schematic diagram illustrating a data recording method;

FIG. 7 is a schematic diagram illustrating a data reproducing method;

FIG. 8 is a schematic diagram schematically illustrating the comparisonbetween the pit position recording and the pit edge recording;

FIG. 9 is a schematic diagram showing an example of a disk format;

FIG. 10 is a schematic block circuit diagram depicting an example of theconfiguration of a recording circuit section;

FIG. 11 is a schematic circuit showing a recording data pattern detectcircuit;

FIG. 12 is a timing chart of signals associated with the recording datapattern detect circuit;

FIG. 13 is a schematic diagram illustrating another example of the datarecording method;

FIG. 14 is a schematic diagram illustrating the configuration of therecording circuit section associated with the data recording method ofFIG. 13.

FIG. 15 is a schematic circuit diagram showing an example of theconfiguration of a reproducing correction circuit;

FIG. 16 is a schematic diagram illustrating a duplicated synchronizationdata pattern;

FIG. 17 is a schematic diagram showing a pattern detect circuit;

FIG. 18 is a schematic diagram illustrating a time-axis correctioncircuit; and

FIGS. 19 (a-c) and 20 are timing charts associated with the time-axiscorrection circuit.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

According to the present invention, a pit edge recording method using asdata the leading edge and the trailing edge of a recording pit isapplied to a recording medium of the thermal recording type. The presentinvention can also be used for a write-once type disk, aphase-transition type disk, and a magneto-optical disk.

In a thermal recording operation, the light energy absorbed when a lightis irradiated into a recording film is transformed into a thermalenergy, which develops a temperature distribution reflecting theinfluence of the heat diffusion strongly and mainly depending on thethermal conductivity of the recording medium. As a result, a pit isformed corresponding to the temperature distribution. In such arecording process, the effect of the heat diffusion greatly contributesto the shape of the pit. The phenomenon will be described.

In FIG. 1, when a light irradiation is achieved with a recording pulse207 having a pulse width 184 as shown in (a), the surface of a disk isscanned by a beam spot 185 which has an irradiation energy 186 of theGaussian distribution and a finite diameter as shown in (b);consequently, a heat diffusion takes place in the direction of the beamspot movement 187. As a consequence, the temperature distribution 188developed on the disk or the shape of the corresponding pit 189 formedtherein becomes to be asymmetric, namely, extends toward the end of thepit as shown in (c) and (d). In a reproduced waveform 190 attainedcorresponding thereto, as shown in (e), the gradient and the amplituderespectively vary between a leading edge 191 and a trailing edge 192.

Next, relationship between the expansion of the pit 189 due to theinfluence of the heat diffusion and the beam movement distancecorresponding to the recording pulse width are shown in FIG. 2. In (a)and (b), the relationships are plotted for two different recording powervalues A and B (A>B) at a given linear speed,, where the abscissaindicates the distance of beam movement 193. In (a), the ordinaterepresents the length of the pit 189 in the direction of beam spotmovement 187, namely, the pit length 194; whereas, the ordinate of (b)indicates the average width of the pit in a direction orthogonal to thebeam spot movement direction 187, namely, the pit width 195 shows in (d)of FIG. 1. As can be seen from these graphs, the fashion of expansion ofthe pit 189 formed varies between two regions separated by adot-and-dash line 196. That is, when the recording power is fixed, in aregion 216 where the beam movement distance 193 is greater than that ofa boundary 196, the pit length is attended with a fixed amount ofexpansion 197 in a linear relationship not depending on the beammovement distance. Furthermore, the pit width 195 also has acharacteristic to reach a fixed saturation value. The amount ofexpansion increase as the recording power becomes stronger and decreasesas the linear speed is increased. On the other hand, in a region wherethe beam movement distance 197 does not exceed that of the boundary 196,both of the pit length and the bit width develop a nonlinearrelationship. A qualitative interpretation of the characteristics abovewill be now described. When the light spot 185 scans the surface of adisk, in a region where the beam movement distance is less than thedistance of the boundary 196, the effect of the expansion andaccumulation of thermal energy due to the heat diffusion towards the endof pit causes the expansion of the pit to be nonlinearly increased asthe beam movement distance becomes longer. However, when the distance ofthe beam movement exceeds that of the boundary 196, since theaccumulation of the thermal energy becomes to be stationary the bitlength has a linear expansion amount and the bit width is fixed.Consequently, since the expansion of the thermal energy is increased asthe thermal conductivity of the recording medium becomes higher, thedistance of the beam movement where the accumulation of the thermalenergy is stationary, namely, the boundary 196 is shifted toward a sideof the longer distance. For the change in the recording conditions,since the influence of the heat diffusion is emphasized as the recordingpower is increased or the linear speed is decreased, the boundary 196also shifts toward the longer-distance side. The characteristics areshown in graphs (a)-(c) of FIG. 3 in which the definition of measuredquantity is represented. Assuming the difference between a centerposition 199 of a pit formed and a center position 198 of the recordingpulse irradiated on the disk surface to be a recording timing variation200, the relationships between the amount of the variation 200 and therecording power are obtained by use of the beam movement distance as aparameter as shown in (b)-(c). The linear speed varies between thegraphs of (b) and (c), namely, the linear speed of (c) is less than thatof (b). The plotted results of (b) and (c) correspond to thecharacteristics shown in FIG. 2. In the region of the linearrelationship, the variation is fixed under conditions that the recordingpower and the linear speed are fixed. On the other hand, in the regionof the nonlinear relationship, it can be seen from the graphs that thevariation or deviation increases as the distance of the beam movementbecomes longer. Two main characteristics are apparent. First, under thecondition of the constant recording power and the fixed linear speed,with respect to the variation in the recording timing, the expansion ofthe pit hardly changes on the side of the leading edge thereof and onlythe expansion on the side of the trailing edge thereof varies dependingon the distance of the beam movement, which is shown in thecharacteristic of (b) or (c) of FIG. 3. Secondly, the increase of thevariation due to the strengthened recording power is caused because thedegree of the expansion of the pit on the trailing edge side is greaterthan that of the expansion on the leading edge side. These twocharacteristics are associated with a fact that the influence of theheat diffusion to the rear side of the pit strongly contributes to theformation of the pit.

Based on the results attained from FIGS. 1-3, a description will begiven of problems in a case where the pit edge recording method isapplied to the thermal recording.

In forming an ideal pit when applying the pit edge recording method tothe thermal recording, the pit is desirably formed in a pit shape 208indicated by a dotted line in (d) of FIG. 1. Namely, when the positionson a disk respectively corresponding to a leading edge 201 and atrailing edge of 202 of a recording pulse 207 of (a) of FIG. 1 matchwith a leading edge 203 and a trailing edge 204 of a pit formed and thewidth of the pit is the same at the leading edge 203 and the trailingedge 204 of the pit, an ideal reproduction waveform 205 ((e) of FIG. 1)is attained and a reproduction pulse 209 ((f) of FIG. 1) detected at anintersection of the waveform 205 and a slice level 206 set to a halfvalue of the amplitude of the reproduced waveform matches with therecording pulse 207 ((a) of FIG. 1). Moreover, in a case where a systemwith modulability including as a series of data a series of pulseshaving the different recording pulse widths, it is necessary to controlthe pit width not to be varied depending on the recording pulse widths.Otherwise, detection of the leading edge and the trailing edge of thepit series becomes to be difficult.

Application of the pit edge recording method to a thermal-recordingmedium is attended with the following problems.

(1) As shown in FIG. 1, since the amplitude of the reproduced waveform190 obtained from an asymmetric pit 189 varies between the leading edge191 and the trailing edge 192 thereof, when detecting an edge at anintersection between the waveform and the fixed slice level 206, eitherthe leading edge of the trailing edge of the pit does not match with theleading edge or the trailing edge of the reproduced pulse, which causesa jitter.

(2) As shown in FIG. 4, when effecting a recording by use of a series ofsuccessive recording pulses like those of (a), since the thermal energyused to record a preceding pit 210 like in a case of (b) is transferredto a position where the succeeding pit 211 is to be recorded because ofan effect of the heat diffusion, the position is preheated and hence apit 211 thus formed has an area greater than that of a pit 212(indicated by a dotted line) recorded with a singular recording pulse,which causes a problem called the thermal interference leading to thejitter.

(3) As shown in (a) of FIG. 1, the pit length is in general greater thanthe distance of the beam movement and hence the associated reproductionpulse width becomes longer than the recording pulse width. Particularly,in a case where the system with modulability is used to increase therecording density by decreasing the interval between the data series asthe beam movement distance corresponding to the recording pulse width ofthe data series is included more deeply in the nonlinear region, sincethe degree of the expansions in the direction of the length and in thedirection of the width respectively vary depending on the distance ofthe beam movement, it is difficult to conduct the ideal pit formationdescribed above in consideration of the variation in recording timing200 shown in (a) of FIG. 3.

For these three problems above, a concrete method to be applied to therecording and the reproduction and a recording medium suitable for thepit edge recording have been considered not to be easily found out and adefinite scheme has not been developed.

In order to apply the pit edge recording method to a thermal recordingmedium, the three problems must be first solved. To this end, accordingto the present invention, a recording medium has been selected and anoptimization is effected on a correction method during a recordingoperation.

First of all, a recording film having a low thermal conductivity hasbeen selected to remove the first and second problems. However, when thethermal conductivity becomes to be too small, the effective recordingsensitively is increased and hence the recording film is deformed due tothe irradiation light power during a data read operation. Consequently,the optimal thermal conductivity is selected to be as great as possiblewithout causing the first and second problems. The upper limit of thethermal conductivity not leading to the first problem of the asymmetricshape of a pit is restricted by a condition that the difference betweenthe amplitude levels respectively of the leading edge 191 and thetrailing edge 192 of the reproduced signal is small. Namely, the upperlimit is selected so as to fully reduce the difference between the widthof the leading edge of the pit and that of the trailing edge of the pitwith respect to the diameter of the beam spot (1/10 or less). On theother hand, the upper limit of the thermal conductivity not leading tothe third problem of the influence of the thermal interference isrestricted by the recording condition under which the influence of thethermal interference becomes to be maximized. That is, the maximum valueis selected such that as shown in (a) of FIG. 4, in a case where afterthe recording pulse 213 corresponding to the maximum data intervalT_(MAX) of the code with modulability utilized, the next recording pulse215 is supplied with an interval of a period of time 214 equal to theminimum data interval T_(MIN), the shape of the pit 211 is not differentfrom that of the pit 212 formed with an isolated pulse.

Utilization of a recording medium satisfying the conditions of thethermal conductivity can solve the first and third problems. However,the second problem cannot be removed. To overcome this difficulty, thefollowing recording correction method i used.

The correction must be effected in consideration of such conditions asthe sensitivity of the recording film, the recording radius or thelinear speed, the density of a data pattern to be recorded, and thelike.

In a case where the linear speed and the recording power are determinedin the linear region 216 in (a) of FIG. 2, when the value obtained bysubtracting an expansion time converted from a fixed expansion 197 froman object pulse width is used as a recording pulse width, a reproducedwaveform associated with the object pit length, namely, the pulse widthcan be detected. Next, a description will be given of an operation toset an optimal recording power at a given linear speed. First, in a caseof a disk rotating at a constant rotary speed, the linear speedcorresponds to a recording position. A method for recognizing therecording position will be described.

A disk includes information called a header portion in which tracknumbers, sector numbers, and the like are stored beforehand. Whenachieving a recording operation, the beam spot is first moved to aposition over a track and a sector in which data is to be written. Thatis, the track number is recognized in any cases and hence the presentposition of the beam spot can be known from the track number. If anexternal scale value can be used as means to identify position of theoptical head, the beam spot is obtainable in the similar fashion.

Recognition of the recording position above enables to optimize therecording power.

The optimization of the recording power is achievable by satisfying thefollowing three conditions for a given linear speed shown in (a)-(b) ofFIG. 2, namely, the characteristic developed at the recording positionobtained according to the method described above. First, the recordingpower must not be set to a large value which may cause the time ofexpansion to exceed the interval of the used data with modulability.Secondly, the recording power should be used in a region where thevariation in the pit length is as small as possible with respect to thechange in the recording power A great fluctuation of the pit lengthleads to a jitter associated with the deviation of the recording power.In the thermal recording, since there exists a threshold value for thethermal recording in general, an unstable recording results when therecording power is too small; consequently, the recording power must beincreased to some extent.

Thirdly, the recording power should be so set not to cause the pit widthto be excessively great. As shown in (b) of FIG. 2, when the recordingpower is increased, the pit width becomes greater. Consequently, in acase where pits are recorded in adjacent tracks in the radial directionof a disk and are then reproduced, an influence of signals extractedfrom pits in the adjacent track, namely, an effect of so-calledcross-talk noise cannot be ignored. The upper limit of the allowable pitwidth is about W/2 when the track pitch is about the diameter W of thebeam spot.

Next, a description will be given of means for correcting the recordingpulse width. The recording pulse width can be reduced by effecting acomputation of a logical OR operation between a data pattern itself anda pattern obtained by delaying the data pattern. This provision enablesthe length of the pit actually recorded in the disk to be associatedwith the reproduction pulse width to be determined.

In the linear region 216, since the recording timing deviation 200 doesnot depend on the recording pulse width and takes a fixed value, aseries of reproduced pulses corresponding to a series of data withmodulability can be attained by use of the correction means.

However, in the nonlinear region 217 of (a) of FIG. 2, since theexpansion varies depending on the recording pulse width, namely, thedistance of the beam movement, in a case where the data interval of theseries of data with modulability is included in the nonlinear region,even when a value obtained by subtracting an expansion time convertedfrom a fixed expansion 197 in the linear region from the data intervalis used as the recording pulse width, the object pit length cannot berecorded; furthermore, the pit width cannot be set to a fixed value.Consequently, a pattern of data with modulability cannot be properlyreproduced.

Next, a first method of recording correction in which the recordingpower is controlled depending on a data pattern will be described.According to this method, when a data pattern associated with pit lengthincluded in the nonlinear region 217 is to be recorded, the recordingpower is controlled depending on the interval of the data patterns so asto locate the plotted data along a dotted line 218 which is an extensionof the linear characteristic. For example, for the recording power B,when recording a data pattern associated with a pit length ₁ included inthe linear region, a length l₂ is calculated by subtracting theexpansion 197 from the beam movement distance l₁ to effect a correctionof the linear region and then a recording pulse corresponding to the l₂is irradiated. On the other hand, when recording a data patterncorresponding to a pit length l₃ included in the nonlinear region, therecording power is set to the value of A which is greater than the powerB. As a result, the linear characteristic 218 is developed for therecording power B, namely, it is only necessary to irradiate a recordingpulse corresponding to a length l₄ attained by subtracting the expansion197 for the linear region from the beam movement distance l₃.

As described above, the correction of the expansion time equal to thatapplied to the linear region enables to record a pit with a pit lengthcorresponding each data interval of the pattern of the data withmodulability; moreover, since the pit width is also increased up to thelevel of the dotted line 219 as shown in (b) of FIG. 2, the object datapattern can be reproduced.

Moreover, as shown in (b) of FIG. 3, the variation 221 in the case 220where the recording pulse width is in the linear region hardly dependson the recording pulse width and takes a fixed value, whereas thedeviation 223 for the recording pulse width 222 in the nonlinear regiongreatly depends on the recording pulse width and takes a valueconsiderably different from the value of the variation 221. Under thesecircumstances, according to the first correction method of the presentinvention, in the recording associated with the nonlinear region, therecording power is set to the value A greater than the recording power Bfor the linear region; consequently, the deviation or variation 224effectively becomes to be similar to the deviation 221 associated withthe recording in the linear region. Since the timing deviation duringthe reproduction is not caused if a fixed recording timing deviationtakes place depending on the recording data pattern, the firstcorrection method of the present invention can minimize the jitter dueto the recording timing deviation.

Subsequently, a description will be given of a second correction methodin which the recording pulse width is controlled depending on the datapattern. In (a) of FIG. 2, the correction in the linear region of therecording power B is achieved in the same fashion as for the firstcorrection method. On the other hand, for example, when recording a datapattern corresponding to the bit length l₃ included in the nonlinearregion, a beam movement distance l₅ is obtained by subtracting anexpansion 225 less than the expansion 197 from the length l₃ and then arecording pulse corresponding to the resultant l₅ is irradiated on tothe disk surface, thereby recording a pit having an object pit length l₃as shown in FIG. 2 and reproducing the object data interval. In thissituation, since the expansion in the nonlinear region varies dependingon the beam movement distance, namely, the recording pulse width, theexpansion 225 as the subtrahend in the subtraction above must becontrolled depending on the data interval. Furthermore, in (b) of FIG.2, when the recording pulse width is controlled according to the datapattern during the recording operation in consideration of the variationin the recording timing associated with the recording pulse width, adata pattern not including a jitter can be reproduced.

The operation to set a recording power depending on the density of therecording pattern as described above can be achieved by means of apattern length judgment circuit using a counter.

Utilization of the recording correction above enables to correct theelongation of the pit length in the thermal recording, namely, theamount of the edge movement. However, the positional fluctuation of theedge itself due to the nonuniformity of sensitivity of the recordingfilm end the variation in the recording power must be eliminated duringthe reproduction. If the position of the edge cannot be properlydetected, the obtained signal becomes to be beyond the datadiscriminating window and hence an error is caused.

According to the present invention, in order to effect a correctionduring the reproduction, the double-pattern system is adopted for astart timing mark generally called a SYNC mark) indicating a position(timing) to start demodulating information corresponding to the leadingand trailing edges of the reproduced waveform. A start timing markdisposed before a series of user data during a data recording operationis detected as a 1-pulse detection signal by use of detect meansassociated with the signal. The reason for the adoption of thedouble-pattern system is that the detention pulse from the leading edgeand that from the trailing edge are separately attained to determine thetime difference therebetween. For an ideal recording medium, thereproduced waveform should be similar to the waveform associated withthe optical pulse used during the recording operation. Actually,however, as described above, because of the nonuniformity of thetemperature distribution in the recording film due to the heatdiffusion, the fluctuation in the write sensitivity, and the like, evenafter the optical pulse irradiation is finished, a pit is formed with anasymmetric shape with a trail. As a result, the gradient of thecorresponding reproduction waveform varies between the leading edge andthe trailing edge thereof. However, it has been confirmed from theconsideration of the influence of the heat diffusion described above andresults of experiments that the gradient is substantially in goodagreement between the leading edges and between the trailing edges,respectively. Consequently, if the edge shift is once correcteddepending on the time difference of the detection signals of therespective start timing signals, the same correction may be applied tothe subsequent data series. For a recording medium controlled in sectorunits, the reliability can be further improved by effecting thecorrection in a sector-by-sector fashion. Incidentally, the method forcorrecting the amount of edge shift during the reproduction based on aprovision to record the same pattern for the leading edge and thetrailing edge of a pit has been proposed in U.S. Ser. No. 878,436.

Referring now to FIG. 5, an embodiment of the present invention will bedescribed. In the configuration of FIG. 1, disk 1 is to be rotated bymeans of a motor 2. According to the present invention, the disk 1 maybe rotated in a constant line speed system in which the rotary speed isvaried depending on a radius associated with a position of the disk 1where an optical head 3 is located or in a constant angular speed systemin which the rotary speed is fixed regardless of the position of theoptical head 3. The optical head 3 can be moved to a position over anobject track of the disk 1. The light emitted from a semiconductor laser4 is passed through a collimate lens 5 to be parallel light flux. Thelight is the fed through a beam splitter 6 and a galvano-mirror 7 to afocus lens 8, which in turn focuses the parallel light flux onto thedisk 1. A light reflected on the disk 1 is fed through the focus lens 8and the galvano-mirror 7 to the beam splitter 6, which reflects thelight. Thereafter, the resultant light is delivered to an auto focusingphotodetector 10. When rotating, the disk 1 vibrates in the vertical andhorizontal or radial directions. For the vertical vibration, a servosignal from the auto focusing photodetector 10 is used to cause thefocus lens 8 to follow the vibration of the disk 1, thereby retainingthe focus on the disk 1. For the vibration in the radial direction, aservo signal from the tracking photodetector 9 is used so as to causethe overall optical head 3 to follow a vibration with a large amplitudeand to change an angle of the galvano-mirror 7 for a vibration with asmall amplitude, thereby locating the optical head 3 over a target trackin any cases. The auto-focusing and the tracking described above can beachieved by use of the conventional servo system and are not directlyrelated to the present invention: consequently, a detailed descriptionthereof will be omitted.

Prior to an explanation of the recording and reproduction, the pit edgerecording method adopted as a recording method of the present inventionwill be described. FIG. 6 is a schematic diagram showing a case wheredata is modulated (encoded) to obtain codes, which are then recorded ona disk; whereas FIG. 7 is a schematic diagram illustrating a case whereinformation recorded on a disk is reproduced to demodulate (decode) theoriginal data.

In the diagram of FIG. 6, data 30 to be recorded is modulated to attaincodes 31 by means of an encoder 13. The encode operation may beaccomplished in any modulation method. Representative codes withmodulability include an FM code, an MFM code, and a run-length limit(RLL) code such as a 2-7 code, an 8-10 code, or a 1-7 code. FIG. 6shows, as an example, a case of the 2-7 code system. The codes 31 areprocessed by an NRZ encoder 14 to be nonreturn-to-zero (NRZ) codes 32.When the NRZ codes are directly recorded on a recording film of the disk1, a pit thus formed generally has a length greater than the width ofthe recording light irradiated onto the disk 1. This phenomenon isdetermined by a balance between a degree of transfer through therecording film of the thermal energy absorbed therein and a meltingpoint resulted from a composition of the recording film and acomposition of a base film on which the recording film is disposed andfurther by a condition of the heat diffusion and the like. In the actualcases, these conditions must be examined through experiments. As anexample, for a write-once type optical disk including a recording filmmade of PbTeSe, when a recording is conducted under conditions of arotary speed of 1800 rotations per minute (rpm), a recording radius of70 mm, and a recording power of 8.5 mW, a width of the actuallyreproduced pulse for a recording pulse wide of 100 ns is 145 ns, namely,an elongation of the pit length is 45 ns in terms of the period of time.As a consequence, in order to correspond the length of the recorded pit35 formed to that of the NRZ codes 32, the pulse width of the recordingcodes 33 is to be decreased in advance. Furthermore, since it isconceivable that the length of the recorded pit 35 is changed dependingon the recording pattern, a correction to increase the power of therecording pulse 34 may be necessary for a short pattern; or, a controlmay be required to be effected on the amount of delay to minimize therecording pulse width in some cases. The width of the recording lightpulse and the power thereof are set by means of the respective settingunits 15-16 under control of a recording corrector 17, thereby causing alaser driver 18 to drive the semiconductor laser 4 so as to form arecorded pit 35. For the encoder, the circuit configuration of theconventional system may be used without modifying the circuit. Concreteconfiguration examples of the NRZ encoder 14, the pulse width settingunit 15, the power setting unit 16, the recording corrector 17, and thelaser driver 18 will be described later in this specification.

Referring now to FIG. 7, a description will be given of a case wheredata 42 is demodulated from the recorded pit 35. The light reflectedfrom the disk 1 changes the quantity of light according to thepresence/absence of the recorded pit 35. In a case where the recordingfilm is a magneto-optical recording film and information is recorded ina form of a magnetic domain, when an analyzer is disposed before thephotodetector 9, the rotation of the polarization plane corresponding tothe direction of magnetization can be converted into a change tn thequantity of light, thereby obtaining a similar reproduction signal 36.By classifying the reproduction signal 36 into one of two value rangesby use of a slice level 37 a reproduced code pulse 38 is obtained. Fromthe leading and trailing edges of the reproduced code 38, correspondingpulses 39-40 are generated to attain a code signal 41. This code signal41 is processed by a decoder effecting an operation opposite to theoperation of the encoder 13 so as to reproduce the original data 42.Since the circuit configuration of the prior art technique need only beused for the decoder, the detailed description thereof will be omitted.

The pit edge recording method above contributes to the increase of thedensity of data thus recorded. This is because of the improvement of therelative resolution of the pit formed and the optical spot used to readthe pit. FIG. 8 is a schematic diagram showing the comparison between apit position recording method in which a round hole is formedcorresponding to a position of "1" of the encoded codes and the pit edgerecording method in which the position of "1" of the encoded codes isassociated with the leading edge or the trailing edge of a pit formed.Let us consider a case where a round hole 50 is formed in associationwith a code 31 in FIG. 8. Since the light spot 51 used to read arecorded pit is distributed in a range greater than the pit, when thedistance between recorded pits is small, the amplitude of a reproducedsignal 52, namely, the degree of modulation 52 cannot be set to asatisfactory value. This tendency becomes more apparent as the recordingdensity is increased. On the other hand, when the code 31 is onceconverted into an NRZ code 32, the reproduced signal 54 generated fromthe pit 53 formed can take a sufficient degree of modulation 52. In thecomparison of FIG. 8, the recording density is assumed to be the sameboth in the pit position recording method and in the pit edge recordingmethod. The recording density of the pit edge recording method can be inprinciple set to be about twice the recording density of the pitposition recording method. In such a case where the double density isimplemented by use of the pit edge recording method, even when theredoes not arise a problem concerning the optical resolution, namely, thedegree of signal modulation, since the width of the data discriminatingwindow used to demodulate the reproduction signal into the original datais reduced to be half the width when the density is not increased it isto be noted that the edge position must be more properly determined. Asa consequence, for such data not requiring a high density as informationof the signals of the header, the data discrimination window may have alarge width so as to use the pit position recording method with theconventional density.

Next, a description will be given of a recording format of a disk foruse with the present invention. FIG. 9 is a schematic diagram showing anexample of a recording format. The configuration of the disk 1 includestracks in a form of concentric circles or spiral shape in which eachtrack is divided into a plurality of regions (sectors). The diagram ofFIG. 9 shows a format of a sector. Each sector begins with a sector mark60 indicating the beginning of sector and the sector mark 60 is followedby a self-clock pull-in pattern 61 to generate a self-clock. A clockgenerated from the pattern 61 is synchronized by use of asynchronization signal pattern 62 so as to detect a reference signal forthe start of demodulation. Through the operation above, a track address63, a sector address 64, and an error correction signal todetect/correct a read error of these addresses are reproduced. Thesedata items constitute header signals 67. Since the header signals arenot to be changed by the user, it will be convenient to pre-format thisportion when the disk is produced. The header and data signals may berecorded in the different modulation methods or by use of differentdepths of holes, respectively. For example, the header signals may berecorded as phase information with a depth equal to 1/4 or 1/8 of thewavelength of the laser light used. Furthermore, the user may record theheader signals 67 in the pit potation recording method and the user datasignals 66 in the pit edge recording method advantageous for a highrecording density.

Although the pre-format part is in general formed on guide grooves forthe tracking operation, a flat portion between guide grooves may also beused for this purpose. Since the flat portion between guide grooves isless influenced by a fluctuation of the laser light during a cuttingoperation of the original disk and other processes, the use of the flatportion is effective to minimize the disk noise during the reproduction.

Referring now to FIG. 10, a description will be given of concretecircuit configuration examples of the NRZ encoder 14, the pulse settingunit 15, the power setting unit 16, the recording corrector 17, and thelaser driver 18, which has not been described in conjunction with FIG.7.

In the system of FIG. 10, the NRZ ,encoder 14 includes a D-typeflip-flop. Each time a leading edge of a code 31 is inputted, theflip-flop operates to reverse the Q output. The circuit connection ofthe flip-flop is generally identical to that used to effect ademultiplication of an input by two. The NRZ code 32 thus converted issupplied to a delay element 45, which delivers having undergone delay ofpreset periods of time to output taps thereof. There may be appliedanother method in which a gate delay is used for the delay element 45.The outputs from the delay element 45 are fed to a selector 46 and oneof the outputs is selected according to an output from a recordingcorrector 17 so as to be inputted to an AND gate 47. Since anotherterminal of the AND gate 47 is supplied with a signal which has notundergone a delay, the width of the pulse generated is decreased by theamount of the delay. The pulse corresponds to the recording code 33 ofFIG. 6. The code 33 is fed to the laser driver 18.

On the other hand, the power of the recording light beam 15 controlledby changing the value of the current source in the laser driver 18,which is configured in a form of a current switch. By changing thepotential of the base of a transistor 48 determining the current valueby means of a D/A converter 44, the light emitting power to be appliedwhen the semiconductor laser 4 is turned on can be varied. For example,when the potential of the base is set to a high value, the potential ofthe emitter of the transistor 48 also becomes to be higher and hence thecurrent flowing through a resistor 49 connected between the emitter anda negative potential (-V) is increased. Consequently, the drive currentdriving the semiconductor laser 4 also increases to obtain a higherlight emitting power. The recording corrector 17 accordingly sets thepulse width and the power depending on a control information 43. As oneof the easiest methods, let us use a read-only memory (ROM) for whichthe track address is an address input and data from the ROM as anoutput; then, the selection of the amount of delay by the selector 46and the specification of input bits to the D/A converter 44 can beeffected. Furthermore, in place of the track address signal 43, a valuefrom an external scale reader 11 may be used; or, based on the number oftracks passed from a reference radius (e.g. the inner-most circle) ofthe disk to the current position, the present location may be recognizedto effect the similar control. In the circuit diagram of FIG. 10, at theend of a data area in which information is to be recorded, a resetsignal 55 is applied to the flip-flop of the NRZ encoder 14, therebypreventing the recording pulses from being mistakenly irradiated ontothe portion of the header of the next sector. In the pit edge recordingmethod, since the recording pulse rises for the first "1" of the dataand fails to the original level for the next "1", if there exist an evennumber of "1's" in the data, the reproduction power is ordinarilyrestored at the end of the data region; however, for an odd number of"I's", the original reproduction power is not restored after the lastdata is written. Consequently, since if the recording power is kept thesame, data of the subsequent sector is destroyed, it will guaranteesafety also to reset the flip-flop immediately when the recording gatesignal specifying the data region becomes to be absent. The gate for thespecification of the recording data region can be easily implemented byuse of a counter to be operated in response to a detection signal of asector mark disposed at the beginning of each sector. According to themethod above, the recording pulse width and the recording power arevaried depending on the recording radius. That is, since the correctionvalue to minimize the recording pulse width and the setting value of therecording power are fixed when the recording radius is determined, thismethod can be effectively applied to the recording in the linear region216 of FIG. 2.

However, as described above, when the data pattern interval is minimizedas the recording density is increased, the recording characteristicenters the nonlinear region 217 of FIG. 2; consequently, the methodabove is not capable of effecting a satisfactory recording correction.This situation necessitates to vary the amount of delay to correct teerecording pulse width or the recording power also depending on thedegree of density of the data pattern.

To this end, as a first correction method, the recording power iscontrolled depending on the data pattern, which will be described inconjunction with an embodiment of the present invention.

FIG. 11 is a circuit example to record data in which the recording poweris increased only for the highest-density pattern, namely, "1001"according to a modulation method to convert the 2-7 codes into the NRZcodes. FIG. 12 shows a timing chart useful to explain the operation ofthe circuit of FIG. 11. The operation of the circuit will be describedwith reference to FIGS. 11-12. DATA-P 32 is a data pattern havingundergone a modulation and is identical to the NRZ code 32 of FIG. 1.The data 32 is synchronized with a leading edge of the recording clockCK-P 150. Counters 151-152, a flip-flop 153, and a shift register 154are initially cleared by a reset signal RESET-N 155 at the "L" levelbefore the data 32 is transferred. The counter 151 has an enable (ENB)terminal connected to the DATA-P so that the count-up operation isenabled only when the data 32 is at the "H" level. When the counter 151is enabled, outputs Q₀ 156, Q₁ 158 from the counter 151 change as shownIn FIG. 12, where Q₀, Q₁, and Q₂ mean outputs of 2⁰, 2¹, and 2²,respectively. The AND gate 159 delivers an output 160 which is set to"H" only when the count value is in the interval of 3. Incidentally, thecounter 151 is so connected to change the output therefrom at afollowing edge of the clock 150. The output 160 from the AND gate 159 isconnected to a reset terminal of the counter 151 and a data (D) terminalof the flip-flop 153 so as to reset the counter 151 when the output 160is set to "H". When the data 32 includes the highest-density pattern"1001", since the leading edge of the data 32 exists in the intervalwhere the AND output 160 is "H", the Q output 161 of the flip-flop 153is set to "H". The Q output 161 is connected to the enable (ENB)terminal of the counter 152. Consequently, when the Q output 161 is setto "H", the counter 151 initiates the count-up operation and then the Q₀162, Q₁ 163, and Q₂ 164 of the counter 152 change as shown in FIG. 12.The output 166 from the AND gate 165 is set to "H" only in the intervalwhere the count value is five, which resets the flip-flop 153 and thecounter 152, As a consequence, the output 161 from the flip-flop 153 isat the "H" level only in the interval where the counter 152 is countingfrom 0 to 5. The Q output 161 is an instruction signal (detection signalof the highest-density pattern) to increase the recording power.

In practice, however, the detection signal 161 of the highest-densitypattern is generated after the generation of the highest-density datapattern and hence the shift register 154 is used to delay the data 32 sothat the highest-density data pattern is located in the interval wherethe signal 161 is at the "H" level. The relationships with respect totime between the delayed data 167 and the highest-density patterndetection signal 161 are as shown in FIG. 12, The signal 161 is used tochange over data to be supplied to the D/A converter 44 of FIG. 10 andthe delayed data 167 is applied in place of the signal 33 of FIG. 10,thereby achieving the object described at the beginning of thespecification. Although the recording power is corrected only for thehighest-density pattern "1001" in the circuit example above, in a casewhere the recording power is also corrected for a data pattern "10001"which is of the second highest density, a circuit which is so connectedthat the output 160 from the AND gate 159 is set to the "H" level whenthe output from the counter 151 is four and that the output 166 from theAND gate 165 is set to the "H" level when the output from the counter152 is six need only be added to the circuit configuration of FIG. 11.

The effect of the first recording correction has been described. Asshown in (b) of FIG. 17, for the amount of deviation of the recordingtiming, there remains a difference between the fixed deviation 221 inthe linear region and the deviation 224 in the nonlinear region afterthe correction, namely, there may exist a case where the recordingtiming deviation cannot be completely corrected.

To remove this troublesome phenomenon, there is applied a method tocontrol the amount of delay so as to decrease the recording pulse widthdepending on the data pattern, which will be described herebelow.

Referring now to FIG. 13, the second recording correction method will bedescribed in comparison with the first recording correction method. Letus consider a case in which the NRZ code 32 converted from the 2-7 codeis recorded. More concretely, as shown in FIG. 13, there are recorded adata pattern 227 having a wide pattern interval and corresponding to therecording characteristic of the linear region 216 and a highest-densitypattern 228 having a short pattern interval and corresponding to therecording characteristic of the nonlinear region 217. In thisdescription, the recording code 33 is attained as a logical productbetween the NRZ code 32 and a delayed NRZ code 226 having a fixed delayτ₁ with respect to the NRZ code 32. The recording code 33 is recordedwith a fixed recording power. Assume the pits 231-232 are formed byrecording pulses 229-230 associated with the data patterns 227-228,respectively. For the pit 231 corresponding to the data pattern 227belonging to the linear region, the expansion and the recording timingdeviation are fixed as described above, for example, for the recordingpulse 229, a pit is assumed to be recorded with an elongation of τ₁ /4on the leading edge side and an elongation of 3 τ₁ /4 on the trailingedge side. On the other hand, in comparison with the pit 231corresponding to the linear region, the pit 232 associated with thehighest-density pattern 228 belonging to the nonlinear region is formedwith the similar elongation or the leading edge side thereof and with adecreased elongation on the trailing edge side; consequently, therecording timing deviation hardly takes place like the deviation 233shown in (b) of FIG. 3. As an example, assuming the expansion on theleading edge side to be τ₁ /4 and that on the trailing edge side to beτ₁ /4. In the first recording correction method, the recording power wasset to a large value for the highest-density pattern 228. The pit 233formed in this case is, as already described in conjunction with (b) ofFIG. 3, attended with a slight deviation 224 on the trailing edge side,which is still less than the deviation 221 in the linear region. Assumehere that due to an increase of the recording power, a pit 233 is formedwith an expansion of τ₁ /2 on the leading edge side as well as on thetrailing edge side. As described above, the reproduced data 234 detectedfrom the pits 231 and 233 recorded according to the first recordingcorrection method are attended with a difference in the recording timingdeviation of τ₁ /4 and hence the jitter 239 is kept remained. To solvethis problem, according to the second recording correction method, thereare provided concrete means to control the amount of delay so as toestablish an agreement of the recording timing deviation; moreconcretely, delay values are separately prepared to determine theleading edge side and the trailing edge side of the recording pulse,respectively. For the amount of delay τ₁ determining the leading edgeside, since the expansion on the leading edge side is of the similardegree in the linear region and the nonlinear region, the delayed NRZcode 226 is directly used. On the other hand, for the amount of thedelay τ₂ determining the trailing edge side, the value is set to zerofor the data pattern 227 belonging to the linear region. For the datapattern 228 belonging to the nonlinear region, based on the recordingcharacteristic of (a) of FIG. 2, a condition is attained to generate apit from which a data pattern interval identical to the data patterninterval of the data pattern 228 can be reproduced by irradiating arecording pulse for which the time difference (τ₁ --τ₂) is subtractedfrom the pattern interval, thereby setting the delay τ₂. That is, theamount of delay τ₂ is varied depending on the data pattern. Using arecording code 236 for which the leading-edge and the trailing edge ofthe recording pulse are respectively determined by the delayed NRZ code226 with the delay τ₁ and the delayed NRZ code 235 with the delay τ₂ ofthe NRZ code, pits 231 and 237 having the dame recording timingdeviation can be formed by the data patterns 227-228, respectively,which enables to reproduce the reproduction data 238 identical to theNRZ code 32. Referring now to FIG. 14, a description will be given of acircuit configuration effecting the second recording correction methoddescribed above. In this configuration, means to set a preset delay τ₁for a data pattern so as to attain a recording code 33 is identical tothe pulse setting unit 15 of FIG. 10. On the other hand, a pulse widthsetting unit 239 is additionally disposed to set an amount of delay τ₂only for the highest-density pattern. In response to a control signalfrom the recording correction unit 17, the pulse width setting circuit239 sets the delay τ₂ obtained from the recording characteristic of (a)of FIG. 12 and delivers the resultant delayed NRZ code 235 with thedelay τ₂ and the NRZ code 32 to an OR gate 240, which in turn outputs aseries of pulses 241 obtained by expanding the pulses of the NRZ code 32by the delay τ₂ on the trailing edge side thereof. Next, the recordingcode 33 and the pulse series 241 are inputted to a trigger terminal Tand a reset terminal R of a flip-flop 242, respectively. The flip-flop242 has a function that with the reset terminal R set to a state of "H",the output Q is set to "H" at a timing of the leading edge of an inputpulse to the trigger terminal T. Furthermore, when the input in thereset terminal is set to "L", the output Q is set to "L" regardless ofthe input to the trigger terminal T. Consequently, this circuit outputsa series of pulses 243 comprising pulses generated at the leading edgeof the recording code 33 and at the trailing edge of the pulse series241. The pulse series 243 is then supplied to a change-over circuit 244.The change-over circuit 244 effects a change-over operation depending ona pattern detection signal 161 such that the pulse series 243 isoutputted only when the highest-density pattern is detected and therecording code 33 is delivered for other patterns. As a result, arecording code 236 appears at the output. In the circuit example above,although the amount of delay τ₂ is set only for the highest-density datapattern "1001", a pulse width setting circuit may be disposed for aplurality of data patterns belonging to the nonlinear region so as tooperate the change-over circuit 244 depending on a detected datapattern. Moreover, it is also possible to combine the first recordingcorrection means and the second recording correction means.

Next, a description will be given of a processing to decode data 42 froma recorded pit 35, namely, an example of a concrete configuration of thereproduction corrector 20. FIG. 15 is a schematic diagram showing aconfiguration example of the reproduction corrector 20. Data convertedinto electric signals through the photodetector 9 is amplified by anamplifier 19 to a desired level. According to the present invention, asshown in FIGS. 6-7, the recording signals are recorded on a disk in aform of variable-length pits corresponding to information to be recordedand the leading edge and the trailing edge of each pit are dealt with asdata. Signals delivered from the amplifier 19 are classified into twovalue ranges by means of a comparator 70 of a differential value outputtype. The threshold value used for the binary value generation issupplied to a reverse input side of the comparator 70. The differentialoutputs are delivered through two paths including a path directlyconnected to the AND gates 71-72 and a path connected thereto via adelay element 73 and a delay element 74, respectively. Consequently, anoutput from the AND gate 71 represents a leading edge detection pulse 39and an output from the AND gate 71 is a trailing edge detection pulse40. In the circuit example of FIG. 15, although a comparator of thedifferential output type is used, the comparator may be of a singleoutput type, namely, of a single-stage configuration. In this case, aninverter with respect to the logic may be disposed so as to use the samecircuit configuration. The leading edge detection pulse 39 and thetrailing edge detection pulse 40 are respectively fed to variablefrequency oscillators (VFO's) 75-76 for generating and synchronizing theself-clock. Outputs from the VFO's 75-76 are delivered to datademodulation start pattern detect circuits (generally referred to asSYNC detect circuits) 77-78, respectively. The pattern agreement signals79-80 respectively detected by the SYNC detect circuits 77-78, theleading edge detection signal 39, and the trailing edge detection signal40 are supplied to a circuit (correction circuit) 81 effecting acorrection with respect to time. A concrete configuration example of thecorrection circuit 81 will be described later. An output from thecorrection circuit 81 is fed to a decoder 82, which in turn decodes thedata. The circuit and method of the decoding may be the same as for theconventional system.

A description will now be given of a demodulation start pattern used inthe present invention. The data demodulation start pattern is recordedat the beginning respectively of the synchronization signal 62 and theuser data 66 in FIG. 9. The data modulation start patterns are providedto appropriately supply a demodulation or decoding timing. In general,in order to detect the pattern, data in shift registers are shifted byuse of a clock generated by a VFO so as to AND small blocks (e.g. 4-bitblocks) of the register outputs, and a majority decision is effectedwith the outputs from the AND gates.

FIG. 16 shows an example of duplicated timing mark patterns. When theleading edge detection signal 39 and the trailing edge detection signal40 are supplied to separate pattern distinction circuits, the agreementsignal 79 from the leading edge and the agreement signal 80 from thetrailing edge are generated at positions shown in FIG. 16. In theexample of FIG. 16, the time difference between these agreement signals79-80 is equivalent to four bits if the edge detection is appropriatelyeffected.

FIG. 17 shows an example of a circuit to detect a timing mark patternfrom the leading edge. Using 8-bit shift register 170-175, a logicalproduct is calculated for the respective small blocks so as to attainthe detection signal from the majority decision circuit 182, Themajority decision circuit 182 may be configured with gates or mayinclude an ROM so as to use as addresses thereof the outputs from therespective AND gates 176 181, thereby obtaining the output data from theROM as the detection signal 79.

In the description above, a recording pit is formed at a proper positiononly through a correction during the recording as shown in FIG. 6,namely description has been given of an ideal case for reproducing aposition of "1" during the recording operation. Actually, however, sincethe position of "1" during the recording operation cannot be correctlyreproduced only by the recording correction in some cases, the width ofthe information discriminating window becomes to be very small and anerror possibly takes place if a demodulation is directly effected. Toovercome this difficulty, the demodulation start timing pattern disposedin the duplicated form is effectively used to automatically correct avariation in the position of an edge of a user data series following thedemodulation start timing pattern, which will be described herebelow.

FIG. 18 is a schematic diagram showing a configuration example of thecorrecting circuit 81 of FIG. 15. The pattern agreement signal 79 fromthe leading edge is supplied to a delay element 101 delivering aplurality of delayed outputs. The outputs 102-105 are delivered to ANDgems 106-109, respectively. In the other hand, the pattern agreementsignal 80 from the trailing edge is supplied to a buffer circuit 110having an amount of delay equal to a delay amount of one of the ANDgates 106-109 and to AND gates 106-109. The outputs 111-114 from the ANDgates 106-109 are delivered to data (D) terminals of flip-flops 116-119,respectively. A trigger (T) terminal of each of the flip-flops 116-119is supplied with an output 115 from the buffer 110. Referring now toFIGS. 19-120, the operation of the circuit of FIG. 18 will be described.FIG. 19 shows the generation timing of the pattern agreement signal 79from the leading edge and that of the pattern agreement signal 80 fromthe trailing edge. In FIG. 19, a case where an agreement signal 80 isgenerated with a delay shorter by α than the normal delay 4T, namely,4-bit clock delay, a case where an agreement signal 80 is generated withthe normal delay, and a case where an agreement signal 80 is generatedwith a delay longer by 8 than the normal delay are shown in (a), (b),and (c), respectively. If the situation is always as shown in (b) ofFIG. 19, the time-axis correction need not be effected at all to use thelogical sum (OR'ed result) of the leading edge detection signal 39 andthe trailing edge detection signal 40 as the code series 41; however, inthe case of (a) or (c) of FIG. 19, it is necessary to effect a timecorrection equivalent to α or β before the logical sum is calculated togenerate the code series 41. FIG. 20 shows the operation of the circuitof FIG. 18 in the case of (a) of FIG. 19. The delayed outputs 102-105are delayed with an equal amount of delay therebetween. Consequently, inthe case of FIG. 19, the delayed output 103 can be used as a delayedoutput to be ANDed with the agreement signal 80 from the trailing edge.As a result, only the output 112 from the AND gate 107 is "H" during theagreement time so as to set the Q output from the flip-flop 117 to "H".Namely, in the circuit of FIG. 18, only the AND gate 125 is opened amongthe AND gates 124-127. On the other hand, the leading edge detectionsignal 39 is fed to the delay element 128 and only the delayed output131 selected from the delayed outputs 130-133 is passed to the AND gate125. If the delayed output 131 is delayed by a period of time equivalentto o of FIG. 6, a correction of the error o can be effected for the userdata series 66 following the agreement signals 79-80. In FIG. 12, thetrailing edge detection signal 40 is also passed through the delayelement 134. This is because about half the maximum delay time of thedelay element 128 is provided for the trailing edge detection signal 40so as to effect the correction thereof at a point further advanced intime. After the correcting operation is thus completed, a logical sum ofthe leading edge detection signal 39 and the trailing edge detectionsignal 40 are obtained by an OR gate 135, which generates a sequence ofdata series. Incidentally, without calculating the logical sum, theleading edge detection signal 39 and the trailing edge detection signal40 may be supplied to separate data demodulation circuits to achieve theobject processing.

A description has been given of the operations of the respectivecomponents of the optical system and recording/reproduction signalprocessing system constituting the optical disk recording/reproductionapparatus of FIG. 5. Next, operations for actually recording andreproducing data on and from the disk 1 will be described according tothe operation sequence.

The disk 1 is ordinarily housed in a cartridge so as to be mounted on aspindle of the motor 2 or on a spindle in a magnet chuck system havingsuch an automatic spindle adjusting mechanism as that used in a compactdisk. Moreover of the optical head 3 is conducted by a linear motor.After the disk 1 is mounted on the spindle, the motor 2 starts rotating.When the motor rotation speed reaches a stationary state or a fixedvalue, a rotation OK signal is sent to the controller so as to turn thesemiconductor laser 4 on and to apply the reproduction power onto therecording film of the disk 1. The auto focus servo is activatedthereafter and then the tracking servo is started to follow guidegrooves formed in the disk 1, which enables to read information from theheader portion preformatted on the disk 1. Through the sequence above,the recording/reproduction control section 12 can recognize the trackaddress and the sector address where the light beam spot is currentlylocated. The positioning of the optical head to a track for therecording operation can be achieved by the prior art method. That is,based on an external scale 11 or the count of the zero-crossing pointsof the signal obtained when the optical head passes a track, a roughpositioning of the optical head is achieved to confirm the track addressand then the optical head is moved over several tracks by means of thegalvano mirror 7. After the optical head s located at an object track,the recording data is recorded in the track. The recording pulse widthand the recording power are set depending on a track number or anexternal scale value and by use of the power setting circuit (FIG. 11)according to the recording pattern. Specification of a recording area inan object sector is effected by generating a recording gate through aclock pulse count control based on the detection pulse of the sectormark 60 or the synchronization signal 62 in the head signal field 62.When recording pulses are irradiated on the disk 1, the gain of the autofocus servo and the tracking servo is increased; consequently, for astable tracking operation, there has been used a method in which thegain is lowered during the recording operation. In the case of the pitedge recording, since the recording power on average is increased ascompared with the case of the pit position recording, the reduction ofthe gain must be emphasized. The actual values must be set inconsideration of various conditions such as the modulation method andthe recording power.

Also for the reproducing operation, the movement and positioning of thebeam spot is achieved through the similar sequence to that of therecording operation. Variation in the position of the data edge duringthe reproduction is reduced by the corrector 20 to achieve a stable datademodulation.

In the apparatus and method of pit edge recording and reproductiondescribed above according to the present invention, a write-once typedisk is used as a recording medium; however, the same operation can beachieved by use of another type of optical disk medium (such as amagneto-optical disk or a phase-transition type disk). Particularly, ina case of a magneto-optical disk, the strength of an external magneticfield applied for the recording and the reproduction can also becontrolled, like the recording pulse width and the recording power,depending on the recording position and the recording pattern.

According to the present invention, in the method and apparatus of datarecording and reproduction in which the leading edge and the trailingedge of the reproduced waveform are dealt with as data, the recordingpulse width and the recording power are set in consideration of therecording position and recording pattern on a disk, the recordingsensitivity of the disk, and the like, thereby achieving the pit edgerecording. During the reproduction, the duplicated synchronizationsignals are used to correct the amount of variation in the edge positionof the user data. Through the corrections during the recording and thereproduction, influence from the variation in the characteristic of therecording film is minimized, which leads to an effect that a highlyreliable data recording and reproduction can be conducted with a reducededge shift.

While the present invention has been described with reference to theparticular illustrative embodiments, it is not restricted by thoseembodiments but only by the appended claims. It is to be appreciatedthat those skilled in the art can change and modify the embodimentswithout departing from the scope and spirit of the invention.

We claim:
 1. An information recording and reproducing method of apit-shape forming optical recording type comprising the stepsof:modulating an intensity of a laser light by a recording pulsecorresponding to an input modulation signal representative of a datapattern to be recorded on a recording medium; irradiating the modulatedlaser light onto the recording medium; forming a local recording regionof a pit-shape by movement of the laser light on the recording medium;and recording and reproducing information utilizing a leading edge and atrailing edge of the recording region as data; wherein a pulse width ofthe recording pulse of the input modulation signal representative of thedata pattern to be recorded on the recording medium is reduced by afixed value in accordance with a line speed of the laser light on therecording medium so as to set a movement distance of the laser light onthe recording medium shorter by a fixed value than a length of therecording region corresponding to the data pattern to be formed on therecording medium originally; and when the movement distance of the laserlight on the recording medium and the length of the recording regionformed by the movement of the laser light are in a non-linearrelationship, increasing an output of the laser light and/or decreasinga reduction value of the pulse width.
 2. A method according to claim 1,wherein during a reproducing operation, signals respectively associatedwith the leading edge and the trailing edge are detected independentlyso as to correct a time interval between both signals.
 3. A methodaccording to claim 2, further comprising increasing the output of thelaser light when the input modulation signal is a highest-densitypattern.
 4. A method according to claim 2, further comprising detectingthe line speed of the laser light on said recording medium utilizing atrack number written in a header region.
 5. A method according to claim1, wherein the recording medium includes a header signal portion havinginformation preformatted in advance thereon, the header signal portionincluding a synchronization signal, a track address, a sector addressand an error correction code.
 6. A method according to claim 1, whereinthe recording pulse is controlled by use of a signal from an externalscale disposed to detect a position of an optical recording/reproducinghead.
 7. A method according to claim 5, where the header signal portionrecorded on the recording medium in advance is recorded in a differentform than that of data signals forming a local recording region of apit-shape.
 8. A method according to claim 5, wherein the header signalportion is formed by use of a pit position recording method.
 9. A methodaccording to claim 2, wherein as synchronization signals to effect atime-access correction of a data series during a reproducing operation,demodulation start synchronization signals are independently provided ina duplicated configuration in a leading edge and a trailing edge of therecording region.
 10. An information recording and reproducing method ofa pit-shape forming optical recording type, wherein an intensity of alaser light is modulated to a high level/low level by a rectangularrecording pulse in accordance with a data pulse representative of a datapattern to be recorded on a recording medium, the recording medium isscanned by the modulated laser light, a local recording regioncorresponding to the recording pulse is formed by the laser light of thehigh level intensity, and recording and reproduction are performedutilizing a leading edge and a trailing edge of the recording region asdata, the method comprising the steps of:reducing a pulse width of thedata pulse in accordance with a line speed of the laser light on therecording medium; modulating the intensity of the laser light to thehigh level/low level by use of the data pulse having the reduced pulsewidth as the recording pulse; scanning the laser light of the high levelintensity only on the recording medium over a range narrower than thelocal recording region to be recorded on the recording medium inaccordance with the data pulse; and increasing a height of the recordingpulse and/or reducing a value of the pulse width when the scanning rangeof the laser light is too short to cause the scanning range of the laserlight on the recording medium and a width of the recording region formedby the scanning of the laser light to be in a non-linear relationship.11. A method according to claim 10, wherein the recording pulse isobtained by reducing the pulse width of the data pulse by calculating alogical product of the data pulse and a pulse obtained by delaying thedata pulse.
 12. A method according to claim 10, wherein the pulse heightof the recording pulse is increased only when the recording pulse is ahighest-density recording pattern.
 13. An information recording andreproducing method of a pit-shape forming optical recording type whereinan intensity of a laser light is modulated by a recording pulsecorresponding to an input modulation signal representative of a datapattern to be recorded on a recording medium, the modulated laser lightis irradiated on the recording medium, a local recording region isformed by a movement of the laser light on the recording medium, and areproducing pulse is obtained from reflected light by irradiating alight beam on the recorded region, the method comprising the stepsof:(1) rising as the recording pulse, a pulse obtained by reducing apulse width of the input modulation signal by a fixed value inaccordance with a moving speed of the laser light on the recordingmedium when a movement distance of the laser light on the recordingmedium and a length of the recording region formed as a result of themovement are in a linear relationship, and (2) controlling of the pulsewidth of the input modulation signal and/or the intensity of the laserlight to maintain the movement distance of the laser light on therecording medium and the length of the recorded region formed as aresult of the movement in a linear relationship when the movementdistance of the laser light on the recording medium and the length ofthe local recording region formed as a result of the movement are in anon-linear relationship.
 14. An information recording and reproducingapparatus of a pit-shape forming optical recording type comprising:headmeans for at least one of irradiating a laser light corresponding to adata pattern to be recorded on a disk-shaped recording medium to form arecording region corresponding to the data pattern and for irradiating alaser light to obtain a reproduced waveform corresponding to therecording region from the recording medium; converting means forreducing a pulse width of an input modulation signal representative ofthe data pattern to be recorded; means for irradiating the laser lightonly on the recording medium over a range narrower than the recordingregion corresponding to the data pattern to be recorded, by modulatingan intensity of the laser light by the input modulating signal convertedby the converting means; and means for increasing an output of the laserlight and/or reducing a reduction value of the pulse width when amovement distance of the laser light on said recording medium and alength of the recording region formed by a movement of the laser lightare in a non-linear relationship so as to make the relationship betweenthe movement distance of the laser light on the recording medium and thelength of the recording region formed by the movement of the laser lightlinear.
 15. An apparatus according to claim 14, further comprisingcontrol means for controlling one of a pulse height and pulse width ofthe recording pulse in accordance with a recording radius of therecording medium having a disk shape.
 16. An apparatus according toclaim 14, further comprising control means for controlling at least oneof a power and a pulse width of the recording pulse in accordance with adegree of a density of a pattern of information to be recorded.
 17. Anapparatus according to claim 14, further comprising self-clock generatemeans and data demodulation start position generate means.
 18. Anapparatus according to claim 14, further comprising means for generatinga self-clock from a reproduced signal associated with the leading edgeand separate and independent means for generating a self-clock from areproduced signal associated with the trailing edge. .Iadd.
 19. Aninformation recording and reproducing apparatus comprising:a recordingmedium which has a pre-formatted region with at least one header signalincluding a track address and a data recording region which arealternatively arranged along said track; irradiating means forirradiating a radiated beam onto said recording medium; pulse widthsetting means for correcting the width of a pulse, a leading edge and atrailing edge of said pulse corresponding to "1" of a predeterminedcode, respectively, by a predetermined amount in response to a linespeed of said radiated beam on said recording medium; modulating meansfor modulating the strength of said radiated beam from high level to lowlevel by means of a recording pulse from said pulse width setting meanssuch that said leading edge and trailing edge of a pit which is formedin said data recording region by scanning said radiated beam onto saidrecording medium corresponding to "1" of said predetermined code,respectively; and reproducing means for independently detecting signalscorresponding to said leading edge and trailing edge respectively ofsaid pit in response to a reproducing signal which corresponds to saidpit on said recording medium and reproducing data by correcting aninterval of said two signals corresponding to said leading edge andtrailing edge respectively of said pit. .Iaddend..Iadd.20. An apparatusaccording to claim 19, wherein said irradiating means includes anoptical head comprising:laser emitting means driven and controlled by adriving circuit; optical means for focusing a laser light from saidlaser emitting means on said recording means; and photo-electricconverting means for converting a reflected light from said recordingmedium into an electrical signal. .Iaddend..Iadd.21. An apparatusaccording to claim 19, wherein said pulse width setting means comprise:delay means for producing a plurality of code signals which are producedby delaying an NRZ code, said leading edge and trailing edge of said NRZcode corresponding to "1" of said predetermined code respectively, by apredetermined period; selecting means for selecting one of said codesignals from said delay means; and means for making a logical productbetween said selected code signal and said NRZ code. .Iadd.22. Anapparatus according to claim 19, wherein said line speed of saidradiated beam on said recording medium is detected by using said trackaddress read out of said preformatted region by scanning said radiatedbeam onto said recording medium. .Iaddend..Iadd.23. An apparatusaccording to claim 19, further comprising: an NRZ modulator forconverting said predetermined code from said modulator into an NRZ code,said leading edge and trailing edge of said NRZ code corresponding to"1" of said predetermined code, respectively; and reset means forresetting said NRZ modulator by means of a gate signal which indicatessaid data recording region such that said strength of said radiated beamis set to low level at the end of scanning said radiated beam onto saiddata recording region. .Iaddend..Iadd.24. An information recording andreproducing apparatus comprising: a recording medium which has apreformatted region with at least one header signal including a trackaddress and a data recording region which are alternatively arrangedalong said track; irradiating means for irradiating a radiated beam ontosaid recording medium; a modulator for converting the data signal to berecorded into an RLL code; an NRZ modulator for converting said RLL codeinto an NRZ code, a leading edge and a trailing edge of said NRZ codecorresponding to "1" of said RLL code, respectively; pulse width settingmeans for correcting the width of a pulse of said NRZ code by apredetermined amount in response to a line speed of said radiated beamon said recording medium; modulating means for modulating the strengthof said radiated beam from high level to low level by means of arecording pulse from said pulse width setting means such that saidleading edge and trailing edge of a pit which is formed in said datarecording region by scanning said radiated beam onto said recordingmedium corresponding to "1" of said RLL code, respectively; reproducingmeans for independently detecting signals corresponding to said leadingedge and trailing edge respectively of said pit in response to areproducing signal which corresponds to said pit on said recordingmedium and reproducing data by correcting the interval of said twosignals corresponding to said leading edge and trailing edge,respectively, of said pit; and reset means for resetting said NRZmodulator by means of a gate signal which indicates said data recordingregion such that said strength of said radiated beam is set to low levelat the end of scanning said radiated beam onto said data recordingregion, whereby information recorded on said preformatted region isprotected from destruction. .Iaddend..Iadd.25. An apparatus according toclaim 24, wherein said irradiating means includes an optical headcomprising: laser emitting means driven and controlled by a drivingcircuit; optical means for focusing a laser light from said laseremitting means on said recording medium; and photo-electric convertingmeans for converting a reflected light from said recording medium intoan electrical signal. .Iadd.26. An apparatus according to claim 24,wherein said pulse width setting means comprise: delay means forproducing a plurality of code signals which are produced by delayingsaid NRZ code, said leading edge and trailing edge of said NRZ codecorresponding to "1" of said RLL code, respectively, by a predeterminedperiod; selecting means for selecting one of said code signals from saiddelay means; and means for calculating a logical product using saidselected code signal and said NRZ code. .Iaddend..Iadd.27. An apparatusaccording to claim 24, wherein said line speed of said radiated beam onsaid recording medium is detected by using said track address read outof said preformatted region by scanning said radiated beam onto saidrecording medium. .Iaddend..Iadd.28. A method of recording andreproducing information by irradiating a radiated beam onto a recordingmedium, which has a preformatted region with at least a header signalincluding a track address and a data recording region which arealternatively arranged along said track, comprising the steps of:modulating the data signal to be recorded into a predetermined code bymeans of a 2-7 modulating method; correcting a width of a pulse, aleading edge and a trailing edge of said pulse corresponding to "1" ofsaid predetermined code, respectively, by a predetermined amount inresponse to a line speed of said radiated beam on said recording medium;forming a pit, a leading edge and a trailing edge of said pitcorresponding to "1" of said predetermined code, respectively, on saiddata recording region by scanning said radiated beam onto said recordingmedium, the strength of said radiated beam being modulated from highlevel to low level in response to said corrected recording pulse; andindependently detecting signals corresponding to said leading edge andsaid trailing edge, respectively, of said pit in response to areproducing signal which corresponds to said pit on said recordingmedium and reproducing data by correcting an interval of said twosignals corresponding to said leading edge and trailing edge,respectively, of said pit. .Iaddend..Iadd.29. A method according toclaim 28, further comprising the steps of: selecting one code signalamong a plurality of code signals which are produced by delaying an NRZcode, said leading edge and trailing edge of said NRZ code correspondingto "1" of said predetermined code, respectively, by a predeterminedperiod in response to said line speed of said radiated beam on saidrecording medium; correcting said pulse width by making a logicalproduct between said selected code signal and said NRZ code..Iaddend..Iadd.30. A method according to claim 28, wherein said linespeed of said radiated beam on said recording medium is detected byusing said track address read out of said preformatted region byscanning said radiated beam onto said recording medium..Iaddend..Iadd.31. A method according claim 28, wherein said NRZ code islowered by a gate signal which indicates said data recording region suchthat said strength of said radiated beam is set to low level at the endof scanning said radiated beam onto said recording region, the loweringof said NRZ code occurring when said predetermined code is convertedinto an NRZ code, said leading edge and trailing edge of said NRZ codecorresponding to "1" of said predetermined code, respectively..Iaddend..Iadd.32. A method of recording and reproducing information byirradiating a radiated beam onto a recording medium, which has apreformatted region with at least a header signal including a trackaddress and a data recording region which are alternately arranged alongsaid track, comprising the steps of: modulating the data signal to berecorded into an RLL code; lowering an NRZ code by a gate signal whichindicates said data recording region such that the strength of saidradiated beam is set to low level at the end of scanning said radiatedbeam onto said recording region, when said RLL code is converted intosaid NRZ code, said leading edge and trailing edge of said NRZ codecorresponding to "1" of said RLL code, respectively; correcting thewidth of a pulse of said NRZ code by a predetermined amount in responseto a line speed of said radiated beam on said recording medium; forminga pit, a leading edge and a trailing edge of said pit corresponding to"1" of said RLL code, respectively, on said data recording region so asnot to destroy information recorded on said preformatted region byscanning said radiated beam onto said recording medium, said strength ofwhich radiated beam is modulated from high level to low level inresponse to said corrected recording pulse; andindependently detectingsignals corresponding to said leading edge and trailing edge,respectively, of said pit in response to a reproducing signal whichcorresponds to said pit on said recording medium and reproducing data bycorrecting the interval of said two signals corresponding to saidleading edge and trailing edge, respectively, of said pit..Iaddend..Iadd.33. A method according to claim 32, wherein said linespeed of said radiated beam on said recording medium is detected byusing said track address read out of said preformatted region byscanning said radiated beam onto said recording medium..Iaddend..Iadd.34. An information recording and reproducing apparatuscomprising: a recording medium which has a pre-formatted region with atleast one header signal including a track address and a data recordingregion which are alternatively arranged along said track; irradiatingmeans for irradiating a radiated beam onto said recording medium; amodulator for converting the data signal to be recorded into apredetermined code; pulse width setting means for correcting the widthof a pulse, a leading edge and a trailing edge of said pulsecorresponding to "1" of said predetermined code, respectively, by apredetermined amount in response to a line speed of said radiated beamon said recording medium; modulating means for modulating the strengthof said radiated beam from high level to low level by means of arecording pulse from said pulse width setting means such that saidleading edge and trailing edge of a pit which is formed in said datarecording region by scanning said radiated beam onto said recordingmedium correspond to "1" of said predetermined code, respectively; andproducing means for independently detecting signals corresponding tosaid leading edge and trailing edge respectively of said pit in responseto a reproducing signal which corresponds to said pit on said recordingmedium and reproducing data by correcting an interval of said twosignals corresponding to said leading edge and trailing edgerespectively; and wherein said pulse width setting means comprise: delaymeans for producing a plurality of code signals which are produced bydelaying another predetermined code, said leading edge and trailing edgeof said another predetermined code corresponding to "1" of saidpredetermined code respectively, by a predetermined period; selectingmeans for selecting one of said code signals from said delay means; andmeans for making a logical product between said selected code signal andsaid another predetermined code. .Iaddend..Iadd.35. An apparatusaccording to claim 34, wherein said predetermined code is an RLL codeand said another predetermined code is an NRZ code. .Iaddend..Iadd.36.An information recording and reproducing apparatus comprising:arecording medium which has a preformatted region with at least oneheader signal including a track address and a data recording regionwhich are alternatively arranged along said track; irradiating means forirradiating a radiated beam onto said recording medium; a modulator forconverting the data signal to be recorded into a predetermined code;another modulator for converting said predetermined code into anotherpredetermined code, a leading edge and a trailing edge of saidpredetermined code corresponding to "1" of said predetermined code,respectively; pulse width setting means for correcting the width of apulse of said another predetermined code by a predetermined amount inresponse to a line speed of said radiated beam on said recording medium;modulating means for modulating the strength of said radiated beam fromhigh level to low level by means of a recording pulse from said pulsewidth setting means such that said leading edge and trailing edge of apit which is formed in said data recording region by scanning saidradiated beam onto said recording medium correspond to "1" of saidpredetermined code, respectively; reproducing means for independentlydetecting signals corresponding to said leading edge and trailing edgerespectively of said pit in response to a reproducing signal whichcorresponds to said pit on said recording medium and reproducing data bycorrecting the interval of said two signals corresponding to saidleading edge and trailing edge, respectively, of said pit; and resetmeans for resetting said another modulator in accordance with a gatesignal indicating said data recording region such that said strength ofsaid radiated beam is set to the low level at the end of scanning saidradiated beam onto said data recording region, whereby informationrecorded on said preformatted region is protected from destruction; andwherein said pulse width setting means comprise: delay means forproducing a plurality of code signals which are produced by delayingsaid another predetermined code, said leading edge and trailing edge ofsaid another predetermined code corresponding to "1" of saidpredetermined code, respectively, by a predetermined period; selectingmeans for selecting one of said code signals from said delay means; andmeans for calculating a logical product using said selected code signaland said another predetermined code. .Iaddend..Iadd.37. An apparatusaccording to claim 36, wherein said predetermined code is an RLL codeand said another predetermined code is an NRZ code. .Iaddend..Iadd.38. Amethod of recording and reproducing information by irradiating aradiated beam onto a recording medium, which has a preformatted regionwith at least a header signal including a track address and a datarecording region which are alternatively arranged along said track,comprising the steps of:modulating the data signal to be recorded into apredetermined code; correcting a width of a pulse, a leading edge and atrailing edge of said pulse corresponding to "1" of said predeterminedcode, respectively, by a predetermined amount in response to a linespeed of said radiated beam on said recording medium; forming a pit, aleading edge and a trailing edge of said pit corresponding to "1" ofsaid predetermined code, respectively, on said data recording region byscanning said radiated beam onto said recording medium, the strength ofaid radiated beam being modulated from high level to low level inresponse to said corrected recording pulse; and independently detectingsignals corresponding to said leading edge and said trailing edge,respectively, of said pit in response to a reproducing signal whichcorresponds to said pit on said recording medium and reproducing data bycorrecting an interval of said two signals corresponding to said leadingedge and trailing edge, respectively, of said pit; further comprisingthe steps of: selecting one code signal among a plurality of codesignals which are produced by delaying another predetermined code, saidleading edge and trailing edge of said another predetermined codecorresponding to "1" of said predetermined code, respectively, by apredetermined period in response to said line speed of said radiatedbeam on said recording medium; and correcting said pulse width by makinga logical product between said selected code signal and said anotherpredetermined code. .Iaddend..Iadd.39. A method according to claim 38,wherein said step of modulating the data signal into said predeterminedcode includes utilizing 2-7 modulation, and said another predeterminedcode is an NRZ code. .Iaddend.